1. Field of the Invention
This invention generally relates to a method of providing a volatile antioxidant (e.g., butylated hydroxytoluene (BHT) and/or butylated hydroxyanisole (BHA)) to a package with a medical device such as a drug-delivery stent.
2. Description of the Background
Drug delivery stent is becoming a common practice to treat, prevent or ameliorate a cardiovascular condition or a related medical condition. In manufacture of drug coated stent, the drug or drug-polymer formulation is first applied onto the stent as a coating. The stent then undergoes many post coating treatments, which may involve heat, moisture, pressure, sterilized gas, electron beam or radiation. After the stents are packaged, it will face shelf life challenges. For example, if a drug is oxygen sensitive, oxidation degradation may occur during these steps. One of the commonly used methods to circumvent these shortcomings is to include one or more antioxidants in the stent coating formulation. Butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA) are commonly used antioxidant in food industry. For instance, many drugs such as limus family (e.g. everolimus, sirolimus, ABT 578, biorolimus) and paclitaxel are oxygen sensitive. To preserve the drug integrity, antioxidant was introduced into the drug coating formulation. Among them are BHT and BHA.
BHA is a volatile solid with melting temperature of 45 to 63° C. BHT can be sublimated at temperatures under its melting point (70° C.). Studies have shown that in some stent coating processes, up to 40% BHT may be lost during standard ethylene oxide (ETO) sterilization process, which involves heat and moisture.
Therefore, there is a need for the preservation of BHT and/or BHA in a stent manufacturing process. There is another need for the incorporation of BHT and/or BHA into the drug product.
The embodiments described below address the above described problems and needs.